From the desirability of the highest possible cruising speed and at the same time the lowest possible takeoff and landing speed, in modern commercial aircraft the need arises for high lift systems, which during takeoff and landing maneuvers can be activated to increase the lift coefficient. Generally speaking, this takes place by means of lift-enhancing flaps which are deflected into the airflow of the aircraft. In particularly widespread use are a host of different slats or leading edge flaps, as well as wing trailing edge flaps in single or multiple rows, with the aforesaid being arranged so as to be movable relative to the wing.
Movable slats, also referred to as extensible slats or leading edge flaps, for example in the form of so-called Krueger flaps, in a retracted position conform to the wing, and in so doing form, for example, part of the wing leading edge, or can be accommodated on the underside of the wing in a suitably formed recess in order to provide a continuous, flush surface. In one or several extended positions, slats are spaced apart or offset from the leading edge of the wing, thus forming a gap between the slat and the leading edge of the wing. From the incident flow towards the aircraft, high-energy airflow moves through the gap onto the profile top of the wing where it shifts the stall towards larger angles of attack. Leading edge flaps can be deflected into the incident flow towards the aircraft, depending on their design, with or without the formation of a gap. At the same time in both the above-mentioned flaps on the leading edge of the wing both the surface of the wing and its curvature are increased.
Commonly used slats or leading edge flaps, which for the sake of simplicity are hereinafter generally referred to as “lift flaps”, comprise a rigid structure whose shape matches the requirements of the wing configuration for cruise flight without activation of the high lift system (clean wing configuration). In this manner the geometry of the gap between slats and leading edges of wings is determined.
In DE 10 2006 053 259 A1 and WO 2008/058695 A1 a high lift system for a wing of an aircraft is presented, in which for the purpose of increasing lift, lift flaps can be moved from a retracted position to extended positions, where a gap between the high lift flaps and the wing can be opened or closed independently of the position of the high lift flaps. In this manner optionally achieving an improved maximum lift coefficient or an improved glide ratio with less noise generation is possible. From DE 10 2007 063 583 A1 and WO 2009/083255 A1 a high lift system for an aircraft is known in which a lift flap is connected to a wing, and can be adjusted by means of at least two adjustment devices, arranged so as to be spaced apart from each other in spanwise direction, in each case by means of a first lever and a second lever.
In known high lift systems with gap-forming lift flaps the gap formed becomes narrower or tapers off between a front of the lift flap and the leading edge of the wing, when viewed downstream frequently to a minimum gap dimension. However, there is the option of known high lift systems with a gap that does not form a gap that tapers off downstream. This is because the normally rigid lift flap may comprise a shape, positioning and deflection that may be limited by the external (e.g. kinematic) positioning boundary conditions, and thus may not allow an ideal converging gap. In this design significantly reduced aerodynamic lift enhancement is achieved when compared to that of an aerodynamically optimal design with a gap that tapers off in downstream direction. Normally an outer geometry of the lift flap is matched to cruise flight, and the surface facing the leading edge of the wing as a result of installations in the wing cannot assume any desired shape. Generally a convergent-divergent shape may not be aerodynamically optimal because the airflow directed towards the profile top loses part of its speed generated in the gap to the point where the flow exits from the gap.
Correspondingly, there may be a need for a high lift system with at least one lift flap arranged on a wing, and at least one flap adjustment mechanism for moving the lift flap between a retracted and at least one extended position relative to the wing, which high lift system provides an aerodynamic improvement and improves the effect, caused by the lift flap, of shifting the stall on the profile top of the wing to larger angles of attack. In addition, other needs, objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.